IR cameras are best for the places where there is no light, as we know that they are used to detect movement even in dark areas. So if you are going to place a camera in a dark place then IR cameras are the better option.

Is there any reason for me to not purchase IR cameras? At night would you actually see the LED's?

If you are thinking about using IR cameras for security, well, it could be the best choice though there are still downside of getting an IR camera. Of couse, LED's can be seen in dark areas especially at night.